ROS-sensitive cytochrome P450 activity maintains endothelial dilatation in ageing but is transitory in dyslipidaemic mice

1 Risk factors for cardiovascular diseases (CVD) have been proposed to accelerate the vascular endothelial dysfunction that develops during the normal ageing process. The objective of this work was to study the impact of dyslipidaemia (DL) on the dilatory efficacy of the non-NO/non-PGI ₂ endothelium-derived hyperpolarising factor (EDHF) through maturation and ageing. 2 We isolated and pressurised (80 mmHg) gracilis arterial segments from 3, 12 and 20-month-old (m/ o) DL mice expressing the human apolipoprotein B-100 and wild-type (WT) C57BL/6 mice. EDHF-dependent dilatations to acetylcholine (ACh) were measured in the presence of L-NNA (100 μM, NOS inhibitor) and indomethacin (INDO; 10 μM, COX inhibitor). Data are expressed as mean ± s.e.m. 3 EDHF-mediated maximal dilatation of arteries isolated from WT mice declined by 44% with ageing, from 86 ± 3% at 3 months to 66 ± 8% at 12 and 48 ± 4% at 20 months of age (P < 0.05). This decline was magnified by DL to 73%, characterised by an early increased efficacy at 3 m/o (95 ± 2%, P < 0.05) and a worsening of the dysfunction at 20 m/o (26 ± 2%, P < 0.05). 4 17-Octadecynoic acid (17-ODYA), a cytochrome P450/epoxygenase inhibitor, reduced by 56% (P < 0.05) ACh-induced EDHF-dependent dilatation of arteries isolated from 3 m/o DL - but not WT - mice, an effect of 17-ODYA disappearing in older DL mice. 17-ODYA, however, reduced (P < 0.05) ACh-induced EDHF-dependent dilatation in arteries isolated from 12 m/o WT mice by 35% and from 20 m/o WT mice by 31% (P < 0.05). 5 Reactive oxygen species production was increased in arteries isolated from 12 m/o DL mice. The antioxidant N-acetyl-L-cystein (NAC) restored the 17-ODYA-sensitive responses in arteries isolated from 12 - but not 20 - m/o DL mice (84 ± 3% from an E _max of 57 ± 8%; P < 0.05). NAC did not affect the dilatation of arteries isolated from WT mice. 6 Our data suggest that the decline in EDHF-dependent dilatation is hastened by DL despite the early expression of a 17-ODYA-sensitive pathway increasing the efficacy of the non-NO/non-PGI ₂ endothelium-dependent dilatation. Acute free radical production contributes to the endothelial dysfunction in the presence of DL only, by abrogating this latter pathway. This 17-ODYA-sensitive pathway, however, appears in 12 m/o WT mice and remains active at 20 m/o.